The present invention relates to a photoelectric sensor capable of recording light information on an information recording medium in the form of visible information or electrostatic information. More specifically, the present invention relates to a photoelectric sensor having on an electrode a photo-induced current amplifying layer which has photo-induced current amplifying action and/or injection current stabilizing action. The present invention also relates to an information recording system including the photoelectric sensor and an information recording medium, and to an information recording and reproducing method which employs the information recording system. More particularly, the present invention relates to an information recording system including a photoelectric sensor having a photo-induced current amplifying layer that markedly amplifies the information recording performance with respect to an information recording medium, thereby making it possible to obtain a predetermined image density and eliminate unevenness of the recorded image and generation of image noise, and also relates to an information recording and reproducing method which employs the information recording system.
There has heretofore been an information recording and reproducing method in which a photoelectric sensor having a photoconductive layer provided with an electrode on the front side thereof is disposed to face, on an optical axis, an information recording medium having an electric charge retaining layer provided with an electrode on the rear side thereof, and exposure is carried out with a voltage being applied between the two electrodes, thereby enabling electrostatic charge corresponding to the incident optical image to be recorded on the electric charge retaining layer, and then the recorded electrostatic information is reproduced by toner development or electric potential reading method, as described, for example, in Japanese Patent Application Laid-Open (KOKAI) Nos. 01-290366 and 01-289975. There is another conventional information recording and reproducing method in which the electric charge retaining layer in the above-described method is replaced by a thermoplastic resin layer, and after electrostatic charge has been recorded on the surface of the thermoplastic resin layer, heating is carried out to form a frost image on the surface of the thermoplastic resin layer, thereby making the recorded electrostatic charge visible, as described, for example, in Japanese Patent Application Laid-Open (KOKAI) No. 03-192288.
The present applicants have developed an information recording and reproducing method in which the information recording layer of the above-described information recording medium is a polymer dispersed liquid crystal layer, and in which exposure is carried out under voltage application in the same way as the above, and the molecules in the liquid crystal layer are aligned by an electric field formed by a photoelectric sensor, thereby effecting information recording, and the recorded information is reproduced as visible information by transmitted or reflected light. With regard to the information recording and reproducing method, we have filed applications as Japanese Patent Application Nos. 04-3394, 04-24722 and 05-266646. This method enables the recorded information to be made visible without using a polarized light plate.
For these information recording methods, there has been a demand for a photoelectric sensor which enables information recording of higher sensitivity, higher resolution and higher image quality. There has also been a demand for a photoelectric sensor of high resolution and high sensitivity which provides a highly stable base current and photo-induced current and which is free from unevenness of sensitivity and noise, thereby enabling an image to be formed at a predetermined image density without scumming.
It is an object of the present invention to provide a photoelectric sensor used to form information on an information recording medium, which has superior information forming power and improved information recording sensitivity, whereby it is possible to obtain an image of high quality which is free from image density variation, sensitivity unevenness and noise, which are particularly noticeable problems in photoelectric sensors of high resolution and high sensitivity, and to provide an information recording system including the photoelectric sensor, and an information recording and reproducing method which employs the information recording system.